1. Field of the Invention
The present invention relates in general to a method of fabricating materials, and relates in particular to a method of ultra-fine microfabrication using an energy beam to fabricate next generation VLSI devices, ultra-fine structures, quantum effect devices and micro-machined devices, and relates also to evaluating the fabrication properties of the energy beam using the method.
2. Description of the Related Art
Photolithography and photomasking to generate a device pattern on a substrate base have been an essential part of fabrication of semiconductor devices. A photolithographic device fabrication process is based on masking those regions of the substrate base which are not to be etched with a photoresist mask, and etching the base material away from those regions which are not protected by a photoresist mask, thereby producing on the fabrication surface ditches or recesses whose depths are dependent on the duration of etching.
FIGS. 15A-15E illustrate the processing steps (step 1 through step 5, respectively) involved in the conventional technique based on the use of photoresist masking. In step 1, the surface of a substrate base 1 is coated with a photoresist material 2. In step 2, ultraviolet light 4 is radiated on the photoresist material 2 through a photomask 3 placed on top of the coated base 1, thereby transferring device patterns 3a formed in photomask 3 to the photoresist material 2. In step 3, the photoresist material 2 exposed by the photomask 3 is removed in a photographic development process to leave behind only the unexposed regions of the photoresist material on the base 1. In the following step 4, unisotropical etching is carried out to remove the base material from the fabrication surface by using ions or radicals in a plasma etching process on those bare regions of the base 1 not protected by the photoresist material 2. In the final step 5, the photoresist material 2 is removed. These five steps are essential in the conventional technique to duplicate the pattern 3a of the photomask 3 by using photolithography to form ultra-fine ditches or recesses 1c in the surface of the base 1. In general, it is necessary to repeat those basic five steps a number of times to form ditches of different depths in the base 1 before an operative semiconductor device can be produced.
Therefore, throughout the process of conventional microfabrication presented above, various photomasks 3 having different complex photoresist patterns 3a are absolutely essential, and furthermore, lines or holes in the range of 1 .mu.m or less are required in the photomasks, special equipment and effort are required, and both capital and labor expenses associated with the technique are rather high. Even with the best of equipment, the technique is basically not adaptable to microfabrication in the range of nanometers. Also, for the technique to be practical, photoresist material 2 must respond to ultraviolet light or electron beams, thereby limiting the choice of photoresist material which can be used. Further, the use of the technique is not allowed when there is a danger of the photoresist material becoming a contaminant. Further, the success of photolithography is predicated on precise flatness of the surface of the substrate base so that the entire fabrication surface lies on a flat plane, to enable uniform fabrication of the entire surface of the substrate base. When the fabrication surface lacks flatness or smoothness, it is not possible to produce a photoresist film of high uniformity and to produce a precise exposure over the entire surface.
Further, in using the conventional plasma etching process to produce patterns of less than 1 .mu.m in size, because of the collision among the gas particles and charge accumulation on the resist material, too many of the charged particles are deviated from linearity, and strike the surface at some non-perpendicular angles to the surface. Under such conditions, it is difficult to produce deep vertical ditches or recesses having a high aspect ratio (a ratio of depth to width), and furthermore, it is nearly impossible to manufacture three-dimensional structural patterns having a width of less than 1 .mu.m.